Foxboro P0916PW terminal component module

Description

FBM237 / P0916CC
FBM217 / P0916PW
FBM219 / P0917LE
FBM219 / P0917LH

PLC is a device used for industrial production automation control, which can be directly used in industrial environments without taking any measures. However, despite the high reliability and strong anti-interference ability mentioned above, when the production environment is too harsh, electromagnetic interference is particularly strong, or improper installation and use, it may cause program errors or arithmetic errors, resulting in erroneous input and output. This will cause equipment to lose control and malfunction, which cannot guarantee the normal operation of the PLC. To improve the reliability of the PLC control system, On the one hand, PLC manufacturers are required to improve the anti-interference ability of their equipment; On the other hand, it is required to attach great importance to design, installation, and maintenance, and to cooperate with multiple parties in order to improve the problem solving and effectively enhance the anti-interference performance of the system. Therefore, the following issues should be noted during use:

1. Work environment
(1) The temperature PLC requires an ambient temperature of 0-55oC, and should not be placed under components with high heat generation during installation. The surrounding ventilation and heat dissipation space should be large enough.
(2) To ensure the insulation performance of the PLC, the relative humidity of the air should be less than 85% (without condensation).
(3) Vibration should keep the PLC away from strong vibration sources and prevent frequent or continuous vibration with a frequency of 10~55Hz. When vibration is unavoidable in the operating environment, shock absorption measures must be taken, such as using shock absorption adhesive.
(4) Avoid corrosive and flammable gases such as hydrogen chloride, hydrogen sulfide, etc. in the air. For environments with high levels of dust or corrosive gases in the air, the PLC can be installed in a well enclosed control room or cabinet.
(5) The power PLC has a certain resistance to interference caused by power lines. In environments with high reliability requirements or particularly severe power interference, an isolation transformer with a shielding layer can be installed to reduce interference between the equipment and the ground. Generally, PLCs have a DC 24V output provided to the input end. When using an external DC power supply at the input end, a DC stabilized power supply should be selected. Due to the influence of ripple, ordinary rectification and filtering power supplies can easily cause the PLC to receive incorrect information.

2. Interference and its sources in the control system
On site electromagnetic interference is one of the most common and easily affecting factors in PLC control systems, which means addressing the symptoms first, identifying the root cause, and then proposing solutions to the problem. Therefore, it is necessary to know the source of on-site interference.

(1) Interference sources and general classification
The interference sources that affect the PLC control system are mostly generated in areas with drastic changes in current or voltage. The reason for this is that changes in current generate magnetic fields, which generate electromagnetic radiation on the equipment; Magnetic field changes generate current, and electromagnetic waves are generated at high speeds. Usually, electromagnetic interference is divided into common mode interference and differential mode interference according to different interference modes. Common mode interference is the potential difference between a signal and ground, mainly formed by the superposition of the common state (in the same direction) voltage induced by the grid connection, ground potential difference, and spatial electromagnetic radiation on the signal line. The common mode voltage can be converted into differential mode voltage through asymmetric circuits, directly affecting the measurement and control signal, causing component damage (which is the main reason for the high damage rate of some system I/O modules). This common mode interference can be DC or AC. Differential mode interference refers to the interference voltage acting between the two poles of a signal, mainly formed by the coupling induction of spatial electromagnetic fields between signals and the conversion of common mode interference by unbalanced circuits. This interference is superimposed on the signal and directly affects the measurement and control accuracy.

(2) The main sources and ways of interference in PLC systems
a. Strong electrical interference
The normal power supply of the PLC system is supplied by the power grid. Due to the wide coverage of the power grid, it will be subjected to all spatial electromagnetic interference and induce voltage on the line. Especially the changes within the power grid, such as surges caused by knife switch operation, start-up and shutdown of large power equipment, harmonics caused by AC and DC transmission devices, and transient impacts caused by power grid short circuits, are all transmitted to the power source through transmission lines.
b. Cabinet interference
The high-voltage electrical appliances inside the control cabinet, large inductive loads, and chaotic wiring can easily cause a certain degree of interference to the PLC.
c. Interference introduced from signal lines
The various signal transmission lines connected to the PLC control system, in addition to transmitting effective information, will always have external interference signals invading. There are two main ways for this interference: firstly, it is caused by the power supply of the transmitter or the power supply of the shared signal instrument connected in series to the power grid, which is often overlooked; The second is that the signal line is interfered by the induction of spatial electromagnetic radiation, that is, external induced interference on the signal line, which is very serious. Introducing interference from signals can cause abnormal operation of I/O signals and greatly reduce measurement accuracy, and in severe cases, it can cause component damage.
d. Interference from chaotic grounding system
Grounding is one of the effective means to improve the electromagnetic compatibility (EMC) of electronic equipment. Proper grounding can not only suppress the impact of electromagnetic interference but also suppress external interference from equipment; However, incorrect grounding can actually introduce serious interference signals, making the PLC system unable to function properly.
e. Interference from within the PLC system
Mainly generated by the mutual electromagnetic radiation between internal components and circuits in the system, such as the mutual radiation between logic circuits and their impact on analog circuits, the mutual influence between analog and logic circuits, and the mismatch between components.
f. Frequency converter interference
One is that harmonics generated during the start-up and operation of the frequency converter cause conduction interference to the power grid, causing voltage distortion and affecting the power supply quality of the power grid; The second is that the output of the frequency converter will generate strong electromagnetic radiation interference, which affects the normal operation of surrounding equipment.